There are two ways to get notified by Tk events: command and bind. Widgets, which
have a default event type, like pressing buttons, define a command initarg. With it, a
function can be bound to this default event type. This is a function, that will be called
with zero or one parameter, depending on the widget type. For those that use it, this parameter
will be the value of the widget (example value of the scale widget).